For the purpose of use in microlenses for optical image forming systems of on-chip color filters in electronic copying machines, solid-state image pick-up elements, and the like, or use in optical interconnection to replace copper wires, photosensitive resin compositions that can form a transparent fine pattern with a high refractive index are required.
In particular, miniaturization of microlenses used in solid-state image pick-up elements is demanded in conjunction with miniaturization of solid-state image pick-up elements, and microlenses having a higher refractive index are demanded in order to achieve more efficient light concentration. In addition, in order to simplify a process for producing a solid-state image pick-up element, a negative-type photosensitive resin composition for forming a microlens that allows pattern formation in a similar manner as that in a color filter formation method is demanded.
For example, there is a disclosure of a photopolymerization composition prepared using titanium oxide particles coated with silica, which composition can provide a pattern having a high refractive index (for example, see Japanese Patent Application Laid-Open (JP-A) No. 2009-179678). Additionally, there is a disclosure of a composition for solid-state image pick-up elements prepared using a metal oxide particle in which the ratio of silicon atoms on the particle surface is 20% or more, with which composition a high refractive index and excellent pattern formability is achieved (for example, see JP-A No. 2008-185683).